<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>点我</button>

    <script>

        class A {
            click () {
                console.log(this);
            }
            // click = () => {
            //     console.log(this);
            // }
        }

        const instance = new A();

        instance.click(); // instance

        document.querySelector('button').addEventListener('click', instance.click); // dom button

    </script>
</body>
</html>